With the quantity and quality of the world's reserves of copper, nickel, cobalt and molybdenum rapidly diminishing, the metallurgical industry is continually looking for better ways of increasing the recovery of present mineral sources and is vigilant in attempting to develop economically attractive processes to recover metal values from ores believed to be of little economic value. Pelagic sedimentary materials containing significant quantities of metal values have been known since late in the ninteenth century; however, no attempts have been made to recover the metal values therefrom. These pelagic sedimentary materials are considered to be complex ores which do not lend themselves to currently known extractive metallurgical processing techniques. Up to the present time these complex ores, which have been termed "manganese nodules," have only been found on the deep lying floor of the oceans and lakes. Terrestrial ore beds containing manganese, iron, copper, nickel, molybdenum, cobalt and other metal values where the ore has physical characterization similar to ocean floor ores have not as yet been discovered. However, it is not unlikely that the same or similar types of complex ores will be located as terrestrial deposits.
It is known that certain metals may be recovered from ocean floor manganiferous ore deposits. Prior to the present invention it was known that in order to recover high yields of metal values such as copper by leaching from an oxidized manganese ore such as manganese nodules, it is advantageous to reduce the ore. At this point it should be noted that it would be more advantageous to eliminate the reduction step all together since reduction constitutes a step which increases costs. However, many investigators have found it desirable to reduce the ore in order to increase the yields. Because it is advantageous to reduce manganese ores in order to recover various metal values contained therein, there are many prior patents directed to processes for reducing such ores. For example, the following patents assigned to the assignee of the present invention, demonstrate that it is desirable to reduce the manganese dioxide in the nodules to the manganous state in order to recover copper, nickel, cobalt and molybdenum.
U.S. Pat. No. 3,723,095 entitled "Extraction of Copper and Nickel from Complex Ores," by R. R. Skarbo, filed July 16, 1970;
U.S. Pat. No. 3,753,686 entitled "Recovery of Copper, Nickel, Cobalt and Molybdenum from Complex Ores," by T. C. Wilder and J. J. Andreola, filed July 16, 1970;
U.S. Pat. No. 3,736,125 entitled "Two Stage Selective Leaching of Copper and Nickel from Complex Ores," by T. C. Wilder filed July 16, 1970; and
U.S. Pat. No. 3,734,715 entitled "Extraction of Metal Values from Complex Ores," by M. J. Redman, filed July 16, 1970.
It should also be noted that although it was known that it is advantageous to reduce the manganese nodules in order to recover the non-ferrous metal values contained therein, prior to the present invention those skilled in the art failed to come up with a method with the economical advantages of the present invention, despite the vigorous research effort made by others trying to recover metals from manganese nodules. It is believed that others were performing research related to various high temperature reduction processes. It is also believed that there is no other low temperature process in which the nodules do not have to be dried to be reduced. For example in the Skarbo process, of U.S. Pat. No. 3,723,095, some high temperature reduction is employed.
The art also recognized the desirability of employing carbon monoxide as a reducing gas since it is readily available and relatively inexpensive. However, at ambient pressures, carbon monoxide will not dissolve in an aqueous slurry of nodules to the degree required to reduce the nodules to the point where metal values can be leached therefrom.
Manganese dioxide is a reactive species which reacts with many reductants. For example, sulfur dioxide and manganese dioxide react to result in a reaction product in which the manganese dioxide is reduced. Reductants such as sulfur dioxide, however, are undesirable for a number of reasons, one of which is that this reductant, as well as many others, cannot be regenerated efficiently. On the other hand, with the process of the present invention, not only can cuprous ions be regenerated; but also, they can be regenerated with carbon monoxide.
In summation, the mining of the vast reserves of manganese deep sea nodules lying over the ocean floor, could be economically justified, if a more economical process were available to effect separation and ultimate recovery of the copper and nickel elements. The recovery of molybdenum and cobalt from these complex ores is also of economic interest.